Process of producing phosphoric acid



Iafented Nov. 20, 1934 UNITED STATES PATENT OFFICE 1,981,145 PROCESS OF rnon U gme PHOSPHORIC A Maryland No Drawing. Application October 21, 1933, Serial No. 694,639

8 Claims.

The present invention relates generally to the production of phosphoric acid in the form of ortho-phosphoric acid and has for some of its objects to provide for simplicity in the extraction of this acid from phosphate-containing materials and for purity and strength of the acid recovered. As herein described in connection with the examples given, the invention is applied to Florida phosphate rock concentrates. 10 An important feature of the invention is the provision of an improved procedure for the recovery of ortho-phosphoric acid from phosphatecontaining materials, wherein comparativelylow temperatures are used and ortho-phosphoric acid is produced without admixture with the other forms of phosphoric acid namely meta-phosphoric acid and pyro-phosphoric acid.

The treatment of the flotation concentrates may commence with decomposition by sulphuric acid. The pulp thus formed contains, besides ortho-phosphoric acid, other products, including lime salts, particularly calcium sulphate. In accordance with the invention, the usual water leach may be omitted, the ortho-phosphoric acid in the pulp being dissolved or leached out by the use of a water-miscible organic solvent having a boiling point lower than that of water. It will be readily understood from the examples given that the miscibility of the solvent with water may vary within wide limits, but the solvents claimed are all appreciably miscible with water, and miscibility is to be understood with reference to these examples. Ketones, alcohols, ethers and esters are included in the group of solvents having the 5 properties mentioned, and in this group acetone has been found particularly satisfactory. The

leaching may be carried out by the well-known continuous counter-current method, or other suitable method. The material leached out in this matter is ortho-phosphoric acid substantially free from lime salts, and it does not contain impurities which are difficult to remove. according to this invention, however, provide other distinct advantages, one of which is the easy removal of the solvent by evaporation. Further, the organic solvent is evaported at a temperature which does not convert the ortho-phosphoric acid into meta-phosphoric acid and/or pyro-phosphoric acid.

Procedures The solution of ortho-phosphoric acid in the organicsolvent is removed from the solid residue,

as by'filtration, and its subsequent treatment with activated carbon has been found very effective in freeing it from suspended organic matter.

'Among the contaminants'which may be contained sulphide. The subsequent treatment with activated carbon removes in one operation the organic matter, the precipitated arsenic trisulphide and, any excess hydrogen sulphide used. Part of the organic'solvent may be evaporated prior to the removal of the contaminants, and the remaining 5 part driven off after the removal of the contaminants.

Any water-soluble calcium phosphate remaining as part of the residue or filter cake obtained by filtration of the leached phosphoric acid, can 7 be recovered by a water leach.

As a preferred procedure, the ortho-phosphoric acid pulp resulting from the decomposition of the raw material may be first subjected to the usual water leach. The liquor thus formed con ,tains ortho-phosphoric acid and soluble lime salts. After the separation of this liquor from the solid matter, it is concentrated by evaporation and then treated with the organic solvent for extraction of the ortho-phosphoric acid. This procedure has the advantage that the amount of organic solvent required to extract the ortho-phosphoric acid from the impure concentrated liquor is less than that required for directly treating the pulp with the organic solvent.

Should purification from arsenic, etc., be required, this may be accomplished when the ortho-phosphoric acid is in solution in water prior to concentration, or when it is in solution in the organic solvent prior to evaporation of the solvent.

Further features and advantages of the invention will appear in the following examples.

Example 1.-Five portions of Florida phosphate concentrate, each weighing 50 grams, were each treated with a mixture of 23.5 cubic centimeters of concentrated sulphuric acid and 23.5 cubic centimeters of water. This amount of sulphuric acid was less than that required for the 100 complete decomposition of the phosphate present, thereby preventing contamination of theortho-phosphoric acid produced with free sulphuric acid. The resultant pulps were left standing in an air-oven at a temperature of from 110 C. to 120 C. for five hours. The material was then allowed to cool and "ripen for 18 hours. The charges were then removed from the oven and one of them was mechanically agitated for 15 minutes with 250 cubic centimeters of acetone. The resulting acetone solution of ortho-phosphoric acid was filteredv by suction and the filter cake washed with acetone. For each of the remaining charges, the procedure of extracting the ortho-phosphoric acid was the same, but utilized as the solvent the acetone solution resulting from the charge previously treated. The acetone in the filtrate from thelast charge to so undergo treatment was driven off by evaporation, and the-material at thisstage was left in the air-oven at a temperature of from 110 C. to 120 C. for 18 hours, after which a black, syrupy mass of ortho-phosphoric acid was obtained.

For recovering the water-soluble products in the residues -or filtercakes. resulting from the acetone leaching, the filter cake resulting from the charge first leached by acetone, was mechanically agitatedv with 250 cubic centimeters of water, the resulting solution'being then filtered and the filter cake washed withwater. The same procedure wa'sjcarriedbut for. each of the remaining batches, utilizing, however, -as

the extracting liquid thefiltrate' obtained by treatment of theprece'ding batch. The final solution, or filtrate, resulting from the last'of the batches to be so treated, was then evaporated to dryness.

The results are shown in the 'following'table:

The acetone-leached orthoephosphoric acid was free from 'sulphuric-acidfand lime salts, but contained considerable organic matter. The solution from water-leaching contained calcium inonophosphate and some calcium sulphate and was only slightly discolored. These products may be separated by well-known and appropriate methods.

:Erample 2.As theacid resultingfrom the acetone leaching in the first test contained organic matter, the procedure of this example'included the removal of this organic matter. Four portions of 50 grams each of Florida concentrate were treated asin Example 1. The filtrate obtained by leaching'with acetone, was evaporated down to approximately 250 cubic centimeters.

The resulting dark brown solution of orthophosphoric acid in acetone was agitated in a flask with-20 grams of so called Norit A activated carbon. This was continued intermittently during the day. The material was'then left standing overnight.- It'was then filtered and the resiwas freed from this contaminant. grams of Florida concentrate were decomposed ketone.

ing were extracted with water, as previously described. 1

The following table indicates the results of this second example:

Gon- Con- Assay Weight calcu med lated lated grams as as as HQPO narol HaPO-l Percent Grams Percent Florida phosphate concentrate". 200.00 46. 03 92. G6 Acetone leach before adding sodium chlorate 71. 50 89. 26 63.82 69. 32 Water leach 20.00 71.00 14. 20 15.42 Filter cake tails 25. 50 2.38 6. 07 6. UnaccountedfoL" 7. 97 8. 66

I, The cleared ortho-phosphoric acid after chlorate treatment, contained no sulphuric acid.

Example 3.-The Florida'concentrate used in the aforesaid examples assayed 0.0012% AS203 and the ortho-phosphoric acid recovered assayed 0.0008% of this substance. was carried out as a result of which the product Thus, 150

and processed as before, in three equal portions of 50 grams each, to extract the ortho-phosphoric acid by acetone leaching. The liquor was evaporated down to approximately-.200 cubic centimeters, HzS gas was bubbled through the concentrated liquor for several minutes, after which 30 grams of NoritA were introduced. The material was left standing for 18 hourswith an accasional shaking. It was then filtered by suction, no HzS odor being perceived. Most of the acetone was distilled 011 at ordinary pressure from a water bath, this taking approximately twenty minutes. Suction was then applied for fifteen minutes, and the temperature in the distilling flask was allowed to rise to 95 C- The resultingacid was cleared up with sodium chlorate and assayed. The ortho-phosphoric acidcontent was 90.8%. It contained noarsenic.

Tests showed that the acetone used as solvent in the process of the present-invention, can be recovered with but a slight loss by the use of simple and inexpensive condensation equipment.

1 Example 4.--'I-Iere 200 grams of Florida phosphate concentrate were decomposed by sulphuric acid in amountless than that required for the complete decomposition of the phosphate present,

and the decomposed material was dried and allowed .to ripen, all as described in connection with preceding examples. The resulting material was mechanically agitated with methylethyl- The liquor was filtered and the ketone evaporated. This resulted in the material marked Acid in the following table. due was similarly agitated-with'water, thema- -terial resulting from evaporation of the water from the filtered solution being. marked H2O soluble in the table.

The resi- The material marked A third procedure Final residue is the residue from the water leaching.

Example 5.-The procedure was the same as in Example 4, except that ethylacetate was'used as the solvent. The results are given in the following table, in which the significance of the terms in the first column is the same as in the table of Example 4.

Example 6.-The procedure was the same as in Example 4, except that methylacetate was used as the solvent. Thefollowing table shows the results.

' Con- 0011- Weight tents tents in lated as calcucalcu- S03 grams H PO lated as lated as 3 4 HaPO4 H3PO4 Percent Florida phosphate con- Per cent Grams Per cent assay 42. 50 91. 39. 05 42. 40 N11 60. 50 70. 92 42. 90 46. 50 4. 50 0O 3. 10 7. 29 7. 90 Unaccounted for- 2. 90 3. 20

Example 7.-Here methylformate was used to extract the ortho-phosphoric acid from a material obtained by decomposing grams of Florida phosphate concentrate. Except for this, the procedure was the same as before.

The following results were obtained:

Example 8.-The procedure was the same as in the preceding example, except that methylal was usedas the solvent, the results being as fol- 'lows: 1

l Con- Con- Weight tents tents in. lated as calcucalcu- S03 grams H PO lated as lated as 3 Harm H3PO Per cent Florida phosphate con- Percent Grams Percent assay centrate 100. 0 46.1 46.10 27. 9 81.8 22. 82 49. 5 Nil 26.0 68. 7 17. 86 38. 7 5. 5 Final residue 122.0 2. 9 3. 54 7.7 Unaccounted for 1. 88 4. 1

A detailed procedurewhich may be followed when it is desired to first subject the decomposed material to the usual water leach for removalof all of the water-soluble products and to then treat the concentrated water solution with an organic solvent for extraction of the ortho-phosphoric acid, is given in the following example.

Example 9.-200 grams of Florida. phosphate concentrate were decomposed by sulphuricacidin an amount less than that required for oornplete decomposition of the phosphate present, as heretofore described. The decomposed material was leached with water,-the solution was filtered and the residue washed with water. The liquor thus obtained was heated in the air-oven for sixteen hours whereupon a heavy mush-like mass resulted. This material was then removed from the oven, acetone was added to it, and it was left to soak with the acetone for several hours, with occasional stirring. Agitation as in the earlier examples, was not used, as it was found that prolonged standing permitted the finely divided particles .of gypsum to settle and the liquor formed to be easily filtered. The residue obtained by filtration, composed in large part Con- Con- Weight tents tents in lated as calcucalcu- S03 grams H PO4 lated as lated as HPO4 H3PO4 Per cent Florida phosphate con- Per cent Grams Per cent assay centrate..- 200.0 46.1 92.2 c' 80.0 88.4 53. 04 57.5 Nil Calcium pho 47.0 57.6 27.07 29.4 11.9 Residue from H20 1e h. 245.0 1.5 3.68 4.0 Unaecounted for .4 8.41 9.1

The ortho-phosphoric acid solution in acetone can be treated as heretofore described for removal of organic matter and arsenic. If iron is present, this contaminant can be removed by addition of potassium ferrocyanide tothe solution. If desired, all of these impurities can be removed from the aqueous solution of orthophosphoric acid obtained by water-leaching.

Examples 10 and 11.Similar procedures were carried out, using, respectively, ethylalcohol and methylalcohol for extracting the ortho-phosphoric acid from the liquor obtained by first leaching the decomposed material with water. The products obtained by these procedures, including the crude acid and the filter cake, were of similar appearance and approxlmatelyof the same weight as by the procedure of Example 9, wherein ace; tone was used as the solvent.

In all of the preceding examples the amount of sulphuric acid used in the decomposition of the phosphate was less than that required for complete decomposition of the phosphate present. This resulted in products containing no free sulphuric acid. While such contaminant is objectionable when the ortho-phosphoric acid is used 'for food purposes, its presence is not at all deleterious, nor does it diminish the market "value of ortho-phosphoric aci'd, when used as a fertilizer material. Therefore, when the ortho-phosphoric acid is to be used for fertilizerpurposes. a greater amount of sulphuric acid may be used to decompose the phosphatic material, resulting in greater amount of free ortho-phosphoric acid soluble in organic solvents. This is demonstrated by the following examples: v

Example 12. grams of Florida phosphate concentrate were treated with a mixtureof 25.5 cubic centimeters of water and 25.5 cubic centimetersof concentrated sulphuric acid, this amount of sulphuric acidbeing slightly in excess of that required for complete reaction. The decomposed material was heated and allowed to ripen, as heretofore described. It was then 'mechanically agitated with acetone, and was filtered. The acetone was evaporated, resulting in the material marked Acid in the following table. The residuewas similarly agitated with water, the solutionwasfiltered and the water was evaporated,v resulting in the material marked H2O soluble in the table. The material marked Residue is the residue from the water leaching.

Con-

tents calculated as H3PO4 Assay calculated as 1131 04 Weight 3 .03

Unaccounted for Example 13. A*similar procedure was carried out with methylacetate as the solvent, the following results being obtained: V

Example 14.A similar procedure was carried out with ethylether as a solvent,resultingin an extraction of 79.8% of an acid of 91.08% strength.

Examples 15 and 16.Propylether and iso- -propylether'gavev similar results but with lower recoveries.

It is to' be understood that this invention is not limited to the specific proceduresv'cgiven in --the foregoing examples. I

1. In a process of producing ortho-phosphoric acid wherein a phosphate-containing material is decomposed to form ortho-phosphoric acid in admixture with other products, the step consisting'in leachingout-ortho phosphoric acid formed by suchdecomposition with acetone.

2. In .a process of producing ortho=phosphoric acid wherein a phosphate-containing material is decomposed "to form ortho-phosphoric acid in ;.admixture with other products, the steps con- Sisting in contacting the decomposed material with acetone, separating theresulting liquor from the solid 'material, and recovering other watersolubleproducts from said solid material by water'leaching.

3. In a process of producing ortho-phosphoric acid wherein a material containing tri-Calcium phosphate is treated with'sulphuric acid to form ortho-phosphoric acid 'in admixture with watersoluble calcium phosphate andicalcium sulphate, the steps consisting in recovering ortho-phosphoric acid frornthe decomposed material by leaching it with acetone, and recovering soluble calcium -.phosphate' by'leaching the residue with water.

l. Insa process of producing ortho-phosphoric acid wherein a phosphate-containing material is decomposed to form ortho-phosphoric acid in admixture 'with other products, the steps consistingin leaching ;out ortho-phosphoric [acid formed by such decomposition with acetone, and recovering ortho-phosphoric acid from the resulting liquor by evaporation of the acetone;

5. In a' process of producing ortho-phosphoric acid wherein a phosphate-containing material is decomposed tc 'form ortho phosphor-ic acid in admixture with other products and in which orthophosphoric acid andfioth'er water-soluble products are leached out by water from the decomposed .material, thesteps consisting in concentrating the solution. containing ortho-phosphoric acid and other water-soluble products, and extracting'ortho=phosphoric.iacid from the concentrated material'bymeans of asolvent comprising 7 one of the substances of the group containing acetone, methylethylketone, ethylacetate, methylacetate; 'methylfcrmate, .methylal, ethylalco- :hol, methylalcohol, 1 ethylether, ,propylether and isopropylether,

16. f Inra process of producing ortho-pho'sphoric acid wherein a phosphate-containing material is decomposed to form ortho-phosphoric acid in admixture with other products and in which ortho-phosphoric acid and "other water-soluble products areleached out by water from the decomposedmaterial, the'steps consisting in concentrating the solution containing ortho-phosphoric acid and other water-soluble products, and extracting :or-thorphosphoric acid from the concentrated material by means ofacetone.

7. In aprocess of producing ortho-phosphoric acid whereina phosphateacontaining material is decomposed 'to form, ortho-phosphoric acid in admixture Withother products and in which ortho-phosphoric acid and other water-soluble products are leached out by water from the decomposed-material; the steps. consisting in concentrating the-solution containing ortho-phosphoric'acid and other water-soluble .products,

contacting theconcentrated material with a solvent comprising one of the substances of the group containing acetone, methylethylketone,

ethylacetate, methylacetate, methylformate, me-' thylal, ethylalcohol, inethylalcohol, .ethylether,

composed material, the steps consisting in concentrating the solution containing ortho-phosphoric acid and other water-soluble products, contacting the concentrated material with acetone, separating the solution of ortho-phosphoric acid in acetone from the solid material, and

evaporating and recovering the acetone from said solution.

CORNELIUS H. KELLER. 

